1. Field of the Invention
The present invention relates generally to techniques for generating an amplifier""s gain control signal in a digital radio communications system, and more specifically to circuitry and method of generating a control signal that is used to adjust a gain of an AGC (automatic gain control) amplifier to which burst signals are applied.
2. Description of the Related Art
In a radio communications system, a signal radiated from a transmitter is subject to undesirable level changes and hence, it is typical to provide a receiver with an AGC amplifier. In the case of signal transmission in burst, a preamble that precedes a data portion is used to adjust a gain of the AGC amplifier. However, a conventional gain control circuit has suffered from the problem that it is difficult to rapidly converge the gain adjusting operation. This is because the conventional technique has adjusted the gain of the AGC amplifier by way of feedback control. More specifically, the output of the AGC amplifier is compared with a reference level and the comparison result is fed back to the AGC amplifier for controlling the gain thereof. Therefore, with a conventional technique, it is necessary to undesirably elongate the preamble in order to correctly adjust the gain of the AGC amplifier. However, if a total time period of each burst is fixed, the aforesaid conventional approach is objectionable because the extended preamble sacrifices the space reserved for data.
It is therefore an object of the present to provide a circuit for rapidly converging a gain control operation of an AGC amplifier that is provided for amplifying burst signals.
Another object of the present invention is to provide a method of rapidly converging a gain control operation of an AGC amplifier that is provided for amplifying burst signals.
In brief, these objects are achieved by techniques wherein in order to rapidly converge a gain control operation of an AGC amplifier which is provided for amplifying burst signals, a level of an incoming bust signal is detected. Following this, a signal indicative of the level of the burst signal is latched in response to a first latch control signal. On the other hand, an output of the AGC amplifier is derived and a level deviation thereof from a reference level is detected. Subsequently, a signal indicative of the level deviation is latched in response to a second latch control signal. The above-mentioned gain control signal is generated using the two kinds of signals held in the latches.
One aspect of the present invention resides in a circuit for generating a gain control signal for use in controlling a gain of an AGC amplifier via which burst signals are amplified, comprising: first means for detecting a level of a bust signal applied to the AGC amplifier, second means for detecting a level deviation of an output of the AGC amplifier from a reference level; and third means for latching a first signal indicative of the level of the burst signal and latching a second signal indicative of the level deviation, the third means generating the gain control signal using the first and second signals.
Another aspect of the present invention resides in a method of generating a gain control signal for use in controlling a gain of an AGC amplifier via which burst signals are amplified, comprising the steps of (a) detecting a level of a bust signal to be applied to the AGC amplifier, (b) latching a signal indicative of the level of the burst signal in response to a first latch control signal; (c) detecting a level deviation of an output of the AGC amplifier from a reference level; (d) latching a signal indicative of the level deviation in response to a second latch control signal; and (e) generating the gain control signal using the signals latched at steps b) and (d).